Patch antennas may comprise, as an example, one or more conductive patch elements supported relative to a ground plane and radiating in a direction substantially perpendicular to the ground plane. For the purposes herein, the word “radiate” or any form thereof is defined as transmitting electromagnetic waves, receiving electromagnetic waves, or both. Conveniently, patch antennas may be formed by employing printed circuit techniques and a dielectric substrate may have a patch printed upon it in a similar fashion to the printing of microstrip feed lines employed in some layered antennas. Patch antennas are versatile in terms of possible geometries that make them applicable for many different configurations. For example, a patch antenna's shape may be of low profile and rectilinear in nature and thus, its planar structure can take advantage of printed circuit technology. Other advantages may include low weight, low volume, and low fabrication costs. Traditional disadvantages may include a narrow bandwidth, half plane radiation, and a limitation on the maximum gain.
For modern telecommunications applications, the patch antenna's traditional advantages usually outweigh the traditional disadvantages. Apart from the electrical performance of an antenna other factors need to be taken into account, such as size, weight, cost, and ease of construction of the antenna. Depending on the requirements, an antenna can be either a single radiating element or an array of like radiating elements. With the increasing deployment of wireless mobile communication devices, an increasing number of antennas are required for the deployment of mobile access systems. Such antennas are required to be both inexpensive and easy to produce.
As stated earlier, a traditional disadvantage of the patch antenna is its inherent narrow bandwidth. Many methods have been proposed to improve the bandwidth, and these include, as examples, the addition of parasitic patches, either laterally or vertically, the use of a thick dielectric substrate, and the cutting of apertures.
A common microstrip patch antenna has a microstrip feed cut-in at the optimum feed point. Patches having such cut-ins, however, do not necessarily provide good crosspolarization performance. Also, circular polarization is difficult to achieve due to perturbations caused by the inset microstrip lines. It is therefore very important to minimize parasitic effects, such as the aforementioned perturbations, of the feed while maintaining simple manufacturability.
Simplification of circuits that interface with the radiating elements is one way to achieve the goals of decreased size, decreased weight, ease of manufacture, and lowered costs. Power divider, filter, and low noise amplifier circuits are examples of structures that microwave and radio frequency (RF) designers often attempt to integrate with the antenna element. Integration with the antenna element usually results in smaller overall packaging and enhanced system performance. However, the packaging associated with common microwave circuits, for example, makes this integration very difficult when a common coaxial probe feed is used. Thus, it has been an objective of antenna designers to simplify the integration of circuits with the radiating element.
A typical antenna 16 using a coaxial cable is shown in FIG. 1A. An outer conductor 5 of a coaxial cable is terminated through a connector 6 to an antenna ground plane 3. A small clearance 7 in the ground plane 3 permits an inner conductor 4 to extend through a substrate 1 and protrude through a patch element 2, where the inner conductor 4 may be electrically bonded to the topside of the patch element 2. The clearance 7 in the ground plane 3 is created so that the inner conductor is not shorted to the ground plane 3. In this example, the substrate 1 is formed of a material with a predetermined dielectric constant. The patch element 2 is printed on top of the substrate 1. However, the substrate can simply be air, as is shown in FIG. 1B. FIG. 1B illustrates a patch antenna that primarily consists of a rectangular patch element mounted over a ground plane in addition to a coaxial cable. The mounting means may consist of nonconductive spacers, such as bolts, nuts, and washers comprised of nylon or similar material.
FIG. 2 illustrates a layered antenna 17 with an integrated stripline circuit in the form of a two-layer structure. The first end of a probe feed 18 protrudes through a patch element 8 and may be electrically bonded on the topside of the patch element 8, while the second end of the probe feed 18 protrudes through a stripline ground plane 11 and may be electrically bonded to a middle circuit layer 12 between a first dielectric layer 19 and a second dielectric layer 20. The stripline ground plane 11 surrounds the first dielectric layer 19 and the second dielectric layer 20. The probe feed 18 extends through a substrate 9 and ground plane 10. This stripline ground plane 11 is electrically connected to the ground plane 10. A first clearance 21 in the ground plane 10 and a second clearance 22 in the stripline ground plane 11 are created so that the probe feed 18 is not shorted to the ground plane 10, stripline ground plane 11, or both. An inner conductor 15 of a coaxial cable protrudes through the stripline ground plane 11 and may be electrically bonded to the middle circuit layer 12. A third clearance 23 in the stripline ground plane 11 is created so that the inner conductor 15 is not shorted to the stripline ground plane 11. An outer conductor 14 of the coaxial cable terminates at the stripline ground plane 11 by a connector 13. The difficulty with this design stems from the desire to provide an interface for the inner conductor 15 and the probe feed 18 as illustrated while connecting the top and bottom stripline layers in a reliable fashion. Some of these limitations may be overcome using modem plated thru-hole technology. However, unintentional parasitics at the interface between the integrated circuit and the antenna element often thwart the intended function of the integration circuit, the antenna element or both. Therefore, as a precursor to fabrication using plated thru-holes, a prototype is highly desirable in which (a) the interfaces closely represent, in the way of electromagnetic coupling, the assembly when fabricated with plated thru-holes, and (b) features of the generic integrated circuit can be readily altered or tuned in situ. Many solutions to this problem are unreliable due to electrically bonded (e.g., solder) joints that are either blind or nearly blind, to coupled lines whose relative positioning is not visible, and to joints between the probe feed and the surface to which it is bonded.
The present invention seeks to provide a novel feed structure incorporated into an antenna, which overcomes or reduces the aforementioned problems.